This changes the revlog.group and re-implements the localrepo.changeroup
function in terms of it.
revlog.group now takes a list of nodes, and some callback functions
instead of a linkmap.
default = "changelog"
header = header-rss.tmpl
changelog = changelog-rss.tmpl
changelogentry = changelogentry-rss.tmpl
filelog = filelog-rss.tmpl
filelogentry = filelogentry-rss.tmpl